Microcavity discharge device

ABSTRACT

A microcavity discharge device generates radiation with wavelengths in the range of from 11 to 14 nanometers. The device has a semiconductor plug, a dielectric layer, and an anode layer. A microcavity extends completely through the anode and dielectric layers and partially into the semiconductor plug. According to one aspect of the invention, a substrate layer has an aperture aligned with the microcavity. The microcavity is filled with a discharge gas under pressure which is excited by a combination of constant DC current and a pulsed current to produce radiation of the desired wavelength. The radiation is emitted through the base of the microcavity. A second embodiment has a metal layer which transmits radiation with wavelengths in the range of from 11 to 12 nanometers, and which excludes longer wavelengths from the emitted beam.

BACKGROUND OF THE INVENTION

[0001] The invention relates to microcavity devices and moreparticularly to a method and device for producing radiation useful inlithography systems.

DESCRIPTION OF RELATED ART

[0002] Integrated circuits are fabricated using lithography systems witha variety of radiation sources, such as for example mid-ultravioletlithography. These sources produce ultraviolet radiation withwavelengths in the range of 100 to 500 nanometers. The ultravioletradiation is used to expose photoresist during integrated circuitfabrication. Radiation emissions with wavelengths of 253-254 nanometersare produced by known microdischarge lamps using a discharge gas.

[0003] A known microdischarge lamp has a substrate, a cathode plug, adielectric layer, and an anode layer. The lamp has a microcavity etchedin the shape of a cylinder. The microcavity has an open end and a closedend. The microcavity extends through the anode and dielectric layers.The microcavity extends into the cathode layer to form a microcavitybase. The diameter of the microcavity is in the range of 1 to 400microns. The microcavity acts as a container for a discharge gas ofmercury or xenon iodine. The discharge gas is supplied to themicrocavity under pressure. The substrate layer and anode layer areformed of conductive materials. The cathode layer is formed of a dopedsilicon and the dielectric layer is formed of silicon dioxide. Thecathode layer is secured to the substrate layer by an epoxy layer.

[0004] By using a semiconductor material for the cathode layer, uniformvoltages can be formed along the length of the microcavity. A dischargegas that is maintained in the microcavity under pressure and subjectedto electric current emits radiation through the open end of themicrocavity. High energy electrons are released by the discharge gaswhich allows access to higher energy or ion states of gaseous atoms ormolecules.

[0005] It has been suggested to operate a lamp by supplying a dischargegas to a microcavity and applying a constant electrical current of 4milliamps between the anode and substrate layers. The discharge gas issupplied to the microcavity at a pressure of up to 200 torr. The lampemits radiation with wavelengths in the 253 to 254 nanometer range. Thelamp can be used in a lithography system. Radiation emitted from thelamp may be reflected off mirrors and through masks or reticles and ontothe semiconductor wafer surface.

[0006] Ideal reflective surfaces for mirrors used in lithography systemsinclude surfaces formed from molybdenum silicon (MoSi) and molybdenumberyllium (MoBe) compounds. These compounds attain their highestreflectivities, approximately 70%, when reflecting radiation withwavelengths in the 11 to 14 nanometers range. Therefore, what is neededis a microcavity discharge device which produces radiation emissionswith wavelengths of less than 253 nanometers, and more particularlywavelengths in the range of from about 11 to about 14 nanometers.

SUMMARY OF THE INVENTION

[0007] The invention relates to a microcavity device which producesradiation with wavelengths in the extreme ultraviolet region. Inaccordance with one embodiment, the device has a semiconductor plug, adielectric layer, and an anode layer. The dielectric layer electricallyseparates the semiconductor layer from the anode layer. A microcavitywith an open end is formed in the anode layer. The microcavity extendsthrough the dielectric layer and has a base in the semiconductor plug.Optionally, a substrate layer having an aperture aligned with themicrocavity can be formed on the bottom surface of the semiconductorplug.

[0008] The microcavity is filled with a pressurized discharge gas, andthe anode and substrate layers are supplied with a combination ofconstant and pulsed currents. The electrical pulses produce radiationfrom the discharge gas which are emitted from the microcavity throughthe bottom of the semiconductor layer and the aperture of the substratelayer. The radiation can be directed as a beam onto mirrors in anoptical system. The mirrors be formed with highly reflective surfaces.When the discharge gas is xenon, the radiation has wavelength peaks inthe range of from about 11 to about 14 nanometers.

[0009] In accordance with another aspect of the invention, a thin metallayer is located between the semiconductor plug and the substrate layer.When the metal layer is beryllium, the emitted radiation has wavelengthsbetween 11 and 12 nanometers (wavelengths greater than about 12nanometers are absorbed by the beryllium layer).

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] These and other advantages and features of the invention will bemore readily understood from the following detailed description of theinvention which is provided in connection with the accompanyingdrawings.

[0011]FIG. 1 is a top view of a microcavity discharge device fabricatedin accordance with a first embodiment of the invention;

[0012]FIG. 2 illustrates a discharge system fabricated in accordancewith the first embodiment of the invention, and includes a crosssectional view of the device of FIG. 1, taken along line II-II;

[0013]FIG. 3 is a top view of a microcavity discharge device fabricatedin accordance with a second embodiment of the invention;

[0014]FIG. 4 illustrates a discharge system fabricated in accordancewith the second embodiment of the invention, and includes a crosssectional view of the device of FIG. 3, taken along line IV-IV;

[0015]FIG. 5 is a top view of a microcavity discharge device fabricatedin accordance with a third embodiment of the invention;

[0016]FIG. 6 illustrates a discharge system fabricated in accordancewith the third embodiment of the invention, and includes a crosssectional view of the device of FIG. 5, taken along line VI-VI;

[0017]FIG. 7 is a top view of a microcavity discharge device fabricatedin accordance with a fourth embodiment of the invention;

[0018]FIG. 8 illustrates a discharge system fabricated in accordancewith the fourth embodiment of the invention, and includes a crosssectional view of the device of FIG. 7, taken along line VIII-VIII;

[0019]FIG. 9 shows the time intervals and amounts of current supplied tothe discharge devices of FIGS. 1 through 8.

[0020]FIG. 10 illustrates a lithography system fabricated in accordancewith one aspect of the invention.

[0021]FIG. 11 illustrates a second lithography system fabricated inaccordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0022] The present invention will be described as set forth in thepreferred embodiments illustrated in FIGS. 1-11. Other embodiments maybe utilized and structural and functional changes may be made withoutdeparting from the spirit or scope of the present invention. Like itemsare referred to by like reference numbers.

[0023]FIG. 1 shows a microcavity device 100 with a microcavity 112fabricated in accordance with a first embodiment of the invention. Themicrocavfty 112 has a diameter D with an open end in the anode layer 120and a closed end or bottom surface 117. The anode layer 120 is connectedto a power supply via electrical connection 152.

[0024] As shown in FIG. 2, the device 100 has a semiconductor plug 114and a dielectric layer 118. The dielectric layer 118 is located betweenthe plug and the anode layer 120. Thus, the dielectric layer 118separates or electrically isolates the semiconductor plug 114 from theanode layer 120. The device 100 can be fabricated by depositing thedielectric layer 118 on the semiconductor plug 114 and depositing theanode layer 120 on top of the dielectric layer 118.

[0025] The microcavity 112 is formed in the device 100 with the bottomsurface 117 formed in the semiconductor plug 114. The microcavity 112 ispreferably cylindrical. The microcavity diameter D is preferably lessthan 120 microns, and more preferably in a range between 10 and 120micrometers. Other microcavity shapes are also possible. The illustratedmicrocavity 112 is etched or drilled through the anode layer 120 and thedielectric layer 118 to a predetermined distance or depth L from thesemiconductor layer top surface 119. The depth L of the microcavity 112is preferably such that the distance between the microcavity bottomsurface 117 and the semiconductor bottom surface 115 is in the range offrom about 0.2 to about 0.8 microns. The hole depth L may be in therange of from about 20 to about 100 microns. The transmissivity of theclosed end (through the bottom surface 117) may be about 50% for lightat a wavelength of 13.5 nanometers.

[0026] The microcavity 112 acts as a container for a discharge gas 116.The gas 116 may include, for example, xenon. The discharge gas 116 issupplied through the open end of the microcavity 112. In FIG. 2, thedevice 100 is shown inside a pressure system 30 which supplies thedischarge gas 116 to the microcavity 112. Formation of the microcavity112 in a single piece integral semiconductor plug 114 allows themicrocavity 112 to operate under higher pressure. The discharge gas 116may be supplied to the microcavity 112 at a pressure that is greaterthan or equal to 200 torr. The pressure of the gas 116 may be in therange of from about 200 to about 600 torr.

[0027] The semiconductor plug 114 is preferably a highly conductivedoped crystalline silicon or polysilicon cathode material with athickness in the range of 20 to 100 microns. A silicon-based material ispreferred because of its resistance to ion sputtering. The dielectriclayer 118 is preferably a silicon dioxide or aluminum oxide with adielectric strength range of 5 to 10 megavolts per centimeter and athickness range of 4 to 10 microns. The anode layer 120 is preferably ahigh conductivity metal or a doped polysilicon. The anode layer 120should have a resistivity of less than 1×10⁻⁷ Ohms-meter and a thicknessof 4 to 20 microns. The anode layer 120 may be formed of copper, gold,tungsten, aluminum, silver, doped silicon, nickel chromium, or the like.

[0028] The plug 114 and the anode layer 120 are connected to anelectrical source 150 by respective electrical connections 151, 152. Theelectrical charge supplied by the source 150 consists of a smallconstant DC current and a short interval larger pulsed current, asdescribed in more detail below. The DC current establishes a virtualanode plasma in the discharge gas 116. When the discharge gas 116 issubjected to the pulsed current, radiation 170 is emitted from thedischarge gas 116 and exits through the microcavity bottom surface 117.The discharge gas 116 produces high energy electrons when subjected toelectrical currents in the amount and size as described below.

[0029] The pulsed current further allows access to higher energy statesof the gaseous atoms or molecules therein, such as for example Xe⁺¹⁰ andXe⁺¹¹, such that the wavelength of the radiation 170 is less than orequal to 253 nanometers, and may be in the range of approximately 11 to14 nanometers. In a preferred embodiment of the invention, the radiationhas wavelength peaks at 11.3 and 13.5 nanometers. These wavelengths maybe used in extreme ultraviolet lithography systems.

[0030]FIG. 3 shows a microcavity discharge device 101 with microcavity122 fabricated in accordance with a second embodiment of the invention.The microcavity 122 has a diameter D and an open end in the anode layer120 and a closed end or bottom surface 127. The anode layer 120 isconnected to a power source 150 via electrical connection 152. The lowerend of the semiconductor plug 114′ is connected to the source 150 byanother suitable electrical connection 151.

[0031] Device 101 differs from device 100 of FIGS. 1 and 2 by thepresence of metal layer 126 located on the bottom surface 115 of thesemiconductor plug 114′. The metal layer 126 may be formed on the bottomsurface 115 of the semiconductor plug 114′ by a known film growthprocess. The metal layer 126 has a thickness in the range of 0.2 to 0.8microns, preferably about 0.6 microns. The metal layer 126 is preferablyformed from beryllium. After the metal layer 126 is secured to thesemiconductor plug bottom surface 115, the microcavity 122 is thenetched completely through the semiconductor plug 114′. Thus, the base ofthe microcavity 122 is the top surface 127 of the metal layer 126. Thedevice 101 is otherwise operated as described above in connection withFIG. 2. The beryllium layer 126 filters out (excludes) radiation that isoutside the 11 to 12 nanometer range. Consequently, when the radiation171 is emitted through the metal layer 126 the wavelengths are in therange of from about 11 to about 12 nanometers. The transmissivity of theclosed end (through the metal layer 126) may be about 50% for light at awavelength of 11.3 nanometers.

[0032]FIG. 5 is a top view of a microcavity discharge device 102 with amicrocavity 132 fabricated in accordance with a third embodiment of theinvention. The device 102 has a substrate 124. The microcavity 132 has adiameter D with an open end in the anode layer 120 and a closed end orbottom surface 137. The anode layer 120 is connected to a power source150 via electrical connection 152.

[0033] As shown in FIG. 6, device 102 varies from FIGS. 1 and 2 by thepresence of a conductive substrate layer 124 located on the bottomsurface 135 on the semiconductor plug 114. The substrate layer 124 canbe secured or formed as a thin film by chemical or physical vapordeposition or as a metallic layer secured by epoxy or other techniques.An aperture 125 is formed in the substrate layer 124 and is aligned withthe microcavity 132. The substrate layer 124 is connected to the source150 by a suitable electrical connection 151. The substrate layer 124 ispreferably a conductive material with a resistivity of less than 1×10⁻⁷ohms-meter and a thickness of 4 to 20 microns. The substrate layer 124may include copper, gold, tungsten, aluminum, silver, doped silicon,nickel chromium, or the like.

[0034] The aperture 125 has sloped sides 121. The sloped sides 121 forma cone having an angle 123 with respect to vertical which is preferablyin a range between 10 and 30 degrees. The angle 123 is preferably 10degrees. The diameter of the truncated top of the cone 121 may begreater than or equal to the diameter D of the microcavity 132. Theradiation 172 is emitted through the aperture 125 and are directed bythe sloped sides 121. The device 102 is otherwise operated like thedevices 100, 101, shown in FIGS. 1-4.

[0035]FIG. 7 is a top view of a microcavity discharge device 103 with amicrocavity 142 fabricated in accordance with a fourth embodiment of theinvention. The microcavity 142 has a diameter D and an open end in theanode layer 120 and a closed end or bottom surface 147. The device 103has a substrate 124. The anode layer 120 is connected to a power source150 via electrical connection 152. The source 150 is also connected tothe substrate 124 by a suitable electrical connection 151.

[0036] Device 103 varies from FIGS. 5 and 6 by the presence of metallayer 126 located on the bottom surface of the semiconductor plug 114′.The metal layer 126 has a thickness in the range of about 0.2 to about0.8 microns, preferably 0.6 microns. The metal layer 126 may includeberyllium with a thickness of 0.6 microns. After the metal layer 126 issecured to the bottom of the semiconductor is plug 114′, the microcavity142 is then etched completely through the center of the semiconductorplug 114′. The base 147 of the microcavity 142 is the top surface of themetal layer 126. The device 103 is operated as described above inconnection with FIGS. 1 through 6. The metal layer 126 can filter outundesired wavelengths. When the metal layer 126 is beryllium, radiation173 having a wavelength in the range of about 11 to about 12 nanometerswill be emitted through the closed end 147 of the microcavity 142.

[0037]FIG. 9 is a plot of the amount of current versus duration that maybe applied to the discharge devices 100 through 103 of FIGS. 1 through 8to produce radiation with the desired wavelengths. The discharge devicesoperate at lower pulsed currents and are more compact than knowndevices. The x-axis represents time in microseconds, while the y-axisrepresents the current in amps supplied by the external power source150. The DC current can vary between approximately 1 and 3 milliamps andthe pulsed current 62 can vary between approximately 60 and 100 amps ata voltage of approximately 220 volts.

[0038] As shown in FIG. 9, a constant 1 milliamp DC current is suppliedto the devices of FIGS. 1 through 8 (line 61) and a pulsed current ofapproximately 60 amps is supplied to the devices 100 through 103 (line62). The pulsed current 62 may be supplied to the devices at arepetition rate of up to approximately 1×10³ pulses per second toprevent adverse heating. The time between successive pulses should beapproximately 1×10⁻³ seconds or greater. The present invention shouldnot be limited to the preferred embodiments described in detail herein.The duration of the pulsed current 62 may be about 1 microsecond or1×10⁻⁶ seconds or less.

[0039]FIG. 10 illustrates a lithography system 50 constructed with apressure system 30 containing a discharge device 100. The pressuresystem 30 supplies pressurized gas to the microcavity. Radiation 170exits through the bottom of device 100 and strikes a first opticalmirror 56. The embodiment is shown with only a second optical mirror 59although additional mirrors could be added. The second mirror 59reflects the radiation 170 through a mask or reticle 58 to the wafer 54.The wafer 54 is shown on a wafer station 53. The mirrors 56, 59 havereflective surfaces formed from molybdenum silicon (MoSi) or molybdenumberyllium (MoBe) compounds. Such compounds have a peak normal incidencereflectiveness of approximately 70% within a reflectivity bandwidth ofapproximately 1 nanometer. These compounds have high reflectivity in the11 to 14 nanometer spectral wavelength region. In particular,multi-layer MoSi reflecting surfaces have their highest reflectivity inthe 13 to 14 wavelength region and MoBe reflecting surfaces have theirhighest reflectivity in the 11 to 12 wavelength region

[0040]FIG. 11 illustrates a second lithography system 350. The system350 differs from FIG. 10 in that the wafer 54 is located outside thelithography system 350. The wafer 54 is conveyed on a wafer transport360. The radiation 170 is transmitted across the system perimeter 355.The system 350 may be suitably arranged to prevent atmospherecontamination and refraction of the radiation 170.

[0041] Having thus described in detail the preferred embodiments of theinvention, it is to be understood that the invention defined by theappended claims is not to be limited by particular details set forth inthe above description as many apparent variations thereof are possiblewithout departing from the spirit or scope of the invention.Accordingly, the above description and accompanying drawings are onlyillustrative of preferred embodiments which can achieve the features andadvantages of the present invention. It is not intended that theinvention be limited to the embodiments shown and described in detailherein. The invention is only limited by the scope of the followingclaims.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. A microcavity device comprising: an open endfor receiving discharge gas, and a closed end, and wherein saidmicrocavity device is arranged to emit radiation with a wavelength lessthan 100 nanometers through said closed end.
 2. A microcavity device ofclaim 1, wherein said wavelength is in the range of 10 to 15 nanometers.3. A microcavity device of claim 1, wherein said open end has a diameterless than or equal to 120 microns.
 4. A microcavity device of claim 1,further comprising said discharge gas.
 5. A microcavity device of claim4, wherein the pressure of said discharge gas is greater than or equalto 200 torr.
 6. A microcavity device of claim 5, wherein the pressure ofsaid discharge gas is in the range of 200 to 600 torr.
 7. A microcavitydevice of claim 4, wherein said discharge gas includes xenon.
 8. Amicrocavity device of claim 1, further comprising a highly conductivedoped crystalline silicon cathode plug, and wherein said cathode plug islocated between said open end and said closed end.
 9. A microcavitydevice of claim 1, further comprising a highly conductive dopedcrystalline polysilicon cathode plug, and wherein said cathode plug islocated between said open end and said closed end.
 10. A microcavitydevice of claim 1, wherein the material thickness between said closedend and the exterior of the device is in the range of 0.2 to 0.8microns.
 11. A microcavity device according to claim 1, furthercomprising a conductive substrate.
 12. A microcavity device according toclaim 11, wherein said substrate has an aperture.
 13. A microcavitydevice according to claim 12, wherein said aperture has sloped sides.14. A microcavity device comprising: an open end for receiving dischargegas, a closed end, and a metal layer, and wherein said microcavitydevice emits radiation through said metal layer.
 15. A microcavitydevice of claim 14, wherein said closed end is formed by said metallayer.
 16. A microcavity device of claim 14, wherein said metal layerincludes beryllium.
 17. A microcavity device of claim 14, wherein saidradiation has a wavelength in the range of 11 to 12 nanometers.
 18. Amicrocavity device of claim 14, wherein said open end has a diameterless than or equal to 120 microns.
 19. A microcavity device of claim 14,further comprising said discharge gas.
 20. A microcavity device of claim19, wherein the pressure of said discharge gas is greater than or equalto 200 torr.
 21. A microcavity device of claim 20, wherein the pressureof said discharge gas is in the range of 200 to 600 torr.
 22. Amicrocavity device of claim 19, wherein said discharge gas includesxenon.
 23. A microcavity device according to claim 14, furthercomprising a conductive substrate.
 24. A microcavity device according toclaim 23, wherein said substrate has an aperture.
 25. A microcavitydevice according to claim 24, wherein said aperture has sloped sides.26. A method of operating a microcavity discharge device, said methodcomprising the steps of: supplying an electrical current to dischargegas located within said device, said electrical current including aconstant direct current and a pulsed current; and emitting radiationthrough a closed end of said microcavity discharge device.
 27. Themethod of claim 26, wherein said radiation has a wavelength that is lessthan 100 nanometers.
 28. The method of claim 26, wherein said emittingstep includes emitting radiation through a metal.
 29. The method ofclaim 26, further comprising the step of supplying said constant directcurrent at a voltage of approximately 220 Volts.
 30. The method of claim29, further comprising the step of supplying said constant directcurrent in the range of approximately 1 to 3 milliamps.
 31. The methodof claim 29, further comprising the step of supplying said pulsedcurrent in the range of approximately 60 to 100 amps.
 32. The method ofclaim 26, further comprising the step of supplying said pulsed currentwith a duration of approximately 1×10⁻⁶ seconds or less.
 33. The methodof claim 26, further comprising the steps of supplying said pulsecurrent at a rate up to approximately 1000 pulses per second.
 34. Themethod of claim 26, further comprising the steps of spacing said pulsecurrent at approximately 0.001 seconds or greater.
 35. An optical systemcomprising: a microcavity discharge device, said microcavity comprising:an open end for receiving gas, and a closed end, and wherein saidmicrocavity discharge device emits radiation with a wavelength less than100 nanometers through said closed end; and a power supply connected tosaid microcavity discharge device.
 36. An optical system comprising: amicrocavity discharge device comprising: an open end for receiving gas,and a closed end, and wherein said device emits radiation with awavelength less than 100 nanometers through said closed end; and amirror for reflecting said radiation.
 37. An optical system according toclaim 36, wherein said mirror includes molybdenum silicon.
 38. Anoptical system according to claim 36, wherein said mirror includesmolybdenum beryllium.